Sleep Disordered Breathing

Definition and Prevalence
Sleep disordered breathing (SDB) or sleep apnea is characterized by complete or partial cessation of breathing, lasting at least 10s, that occurs repeatedly throughout the night. The respiratory disturbance index (RDI) represents the number of complete pauses (apnea) and partial pauses (hypopnea) in respiration per hour of sleep.

There are two types of apnea: obstructive and central. Obstructive apneas are caused by an anatomic obstruction of the airway during sleep. Patients attempt to breathe and may appear to be choking or gasping for breath; however, despite their respiratory effort the airway is shut down. The obstruction may be located in different areas, but most often it is in the lower pharynx, between the base of the tongue and the larynx. Many patients with obstructive sleep apnea are heavy, loud snorers, as snoring in itself is also a result of a partial obstruction of airflow. In mild to moderate cases, obstructive apnea may be related to body position. Sleeping in a supine position may increase the frequency and severity of the apnea, as the tongue falls back to the anterior neck and oropharynx. Respiratory events may occur in all sleep stages; however, in some patients the length and severity of the events increases during REM sleep.

Central apneas are caused by failure of the central nervous system respiratory centers. Respiratory neurons fail to stimulate the motor neurons that activate the respiration process, resulting in an absence of respiratory effort. Central apnea is common in patients with heart failure or stroke. Many patients have mixed apneas, with both central and obstructive components.

Ancoli-Israel et al. have reported the prevalence of SDB with RDI greater than 10 in 70% of elderly men and 56% of elderly women, respectively, compared to only 15% and 5% of younger men and women, respectively.

Consequences of the Disorder
Patients with SDB stop breathing in their sleep. To start breathing again, they must awaken. Often these awakenings are so brief that they are not recalled the next morning. However, these short repetitive arousals may cause sleep fragmentation, which in turn may lead to excessive sleepiness during the day. The respiratory events may cause oxyhemoglobin desaturation, which may cause morning headaches and decreased cognitive functioning.

SDB is also an independent risk factor for hyper-tension and is associated with obesity and cardiac arrhythmias. In severe cases, SDB has been linked to increased mortality. However, in a review of the literature, Wright et al. claimed that evidence for an association between SDB and morbidity and mortality was not sound, and other confounding factors such as age, body mass index, smoking, and alcohol use were often not properly considered.

Epidemiologic studies have linked SDB in the elderly with cognitive impairment and dementia. Ancoli-Israel et al. found significant associations between SDB and cognitive functioning in community- dwelling elderly, as well as in the nursing home, where severe apnea was significantly correlated with severe dementia.

Clinical Presentation
The two chief complaints of the apnea patient are loud snoring (usually the spouse suffers from this and is motivated to seek help) and excessive daytime sleepiness. Patients usually do not complain of sleep disruption, as they do not remember the nighttime arousals. However, the daytime sleepiness may have extreme consequences, as some patients may fall asleep at work or while driving. Morning headaches, confusion, and cognitive impairment are also common, particularly in the elderly. Some studies have linked these disturbances to the hypoxemia or to the excessive sleepiness.

Risk Factors
Patients with SDB are often obese, although this is less true in the elderly. Smoking has been implicated as a risk factor.

Diagnosis
Sleep disordered breathing (SDB) must be evaluated by an all-night sleep recording. Traditionally, this is done in a sleep laboratory, with a full EEG montage, including a nasal thermistor that records airflow and chest and abdomen movements, and oximetry, to determine oxy-hemoglobin level. Portable equipment that can be set up in the patient’s home is also available. This alternative is particularly appropriate for elderly individuals who may become confused or disoriented or simply uncomfortable while sleeping away from home. Based on the sleep recording, the RDI is computed and treatment options are evaluated. SDB is diagnosed slightly differently in the various sleep clinics, but generally the cutoff point is an RDI greater than 10 to 15.

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